Soldiers are not entitled to commit murder. Where do you get this Kooky idea from?
Odo said that killing your own clone is still murder which doesn't leave room for interpretation, I am pretty sure that if he meant "according to Bajoran law" he would have said so. The station is not under Bajoran law otherwise Sisko would have no authority whatsoever and he would have been the one at Kira's disposal instead of the other way around like it was.
When the Mariposan prime minister burst into the lab and saw Will destroying the clones, he yelled out "Murderers!"
So, I guess killing a clone is not only a crime in Odo's and DS9's jurisdiction but it is also a crime on Mariposa. And since Will was on Mariposa when he committed his acts, presumably Will would have been subject to Mariposan law. At the very least, it would seem that Will did commit crimes under Mariposan law, if not also under Federation/Starfleet laws or regulations.
Couple that with the fact that we know of our characters that they don't just snuff out living things solely for unwarranted personal reasons,.
But there was a personal reason in this instance. Riker felt violated. And he was right about that. The Mariposans cloned him without his consent. But does two wrongs make a right?
Apparently the Mariposans didn't have the abiltity to enforce their law against Riker, so Will got away with it. Plus the mariposans probably committed a crime as well when they took Will's Dna without his consent. I suppose, with that in mind, the Mariposans let bygones be bygones.
It seemed like Picard and Riker had a double standard. When they had a personal or emotional stake in a matter, they made exceptions so as not to have to follow their own (or Starfleet's) principles.
In "Justice", Picard openly admitted that he would be violated the prime directive if he were to save Wesley's life. He had a personal stake in the matter, especially with Beverly nagging at him. As you know, Picard went on to violate the prime directive.
In "Pen Pals", Picard had no problem with letting that alien girl and her people perish because of the prime directive, but Data had a personal stake in the matter. Ultimately, Picard allowed Data and the Enterprise to intervene to save the girl's planet and people, it seemed, as a favor to Data.
In the case of Riker's clone, I don't doubt that Picard was sympathetic to Riker and so did not raise any issues with Riker destroying the clones.
The case of Tom Riker was different than the situation with Will's Mariposan clone.
Picard did seem to operate with a double standard at times. When he or a close crew member had a personal or emotional stake in a matter, he was more than willing to violate his or Starfleet's directives and principles.